This invention generally relates to the field of digital processing of the counting of randomly occurring pulses and more specifically, to the field of high speed digital processing of pulses for neutron coincidence counting. This invention is a result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).
Neutron coincidence counting is of importance in both active and passive non-destructive assay (NDA) instrumentation as coincidence is a unique signature of the fission process. High speed analog detectors, along with digital processing and output, is essential to accomplish accurate time-correlation measurements in the nuclear field and for other fields in which rapidly and randomly occurring pulses are to be accurately detected and counted.
Prior art neutron time-correlation, or coincidence, counting circuits have most notably suffered from limited counting speed and accuracy due in large part to excessive dead times, that is, the period during which input pulses are not being processed. In most prior art devices, this dead-time period ranges from approximately 0.7 to 2.4 microseconds. A good review of counting circuits used in the nuclear materials measurement and safeguards fields is made by J. S. Swansen, P. R. Collinsworth, and M. S. Krick in "Shift-Register Coincidence Electronics System for Neutron Counters," Los Alamos National Laboratory Report LA-8319-MS, April 1980.
Some of the previous designs for coincidence counters have OR'D outputs from several neutron detectors and forwarded the OR output to a single shift register. Thus, once a pulse was loaded into the shift register, the unit was unable to accept additional pulses until the existing pulse in the shift register was shifted into the next bin. In the case of a 1 MHz shift clock, this dead time could approach 1 microsecond.
Previous coincidence counting devices have also commonly employed histogramming memory. Histogramming memory has a bandwidth of only approximately 0.9 MHz, and can result in an unacceptable loss of data. This loss is entirely eliminated in the present invention.
The present invention also provides for the programming of several parameters such as shift register length, shift register clock frequency and background read interval. This programming ability allows the present invention to be mated with various neutron detectors.
It is therefore an object of the present invention to provide a high-performance neutron time-correlation counter that minimizes the dead-time of the device.
It is another object of the present invention to provide a high-performance neutron time-correlation counter having improved counting accuracy.
It is a further object of the present invention to provide a high-performance neutron time-correlation counter that may be used with various neutron detectors.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.